Effect of Reducing and Oxidizing Atmospheres on the PTCR Properties of BaTiO 3

BaTiO3 ceramics containing n-type dopant exhibited no PTCR effect when sintered in a reducing atmosphere. The resistivity jump of up to 3 orders of magnitude appeared after the samples were annealed in air at various temperatures. Subsequent heat treatment of the samples in a reducing atmosphere at 400°C led to a significant decrease in the resistivity jump. The PTCR effect is restored after additional annealing in air at temperatures as low as 400°C. Calculations of oxygen diffusion into the sample suggest that the appearance of the PTCR in BaTiO3 occurs at temperatures much higher than that required to promote fast grain boundary diffusion of oxygen. Thus, the PTCR effect is associated with grain boundary segregation of cation vacancies rather than chemisorption of oxygen.